1. Technical Field
The present invention relates to a lead cutter and a method of fabricating a semiconductor device.
2. Related Art
Semiconductor devices having a plurality of outer leads on the outer periphery of molding resin encapsulating semiconductor chips are fabricated according to the procedures below. First, a semiconductor chip is mounted on a leadframe, and then molded with resin. The process is then followed by deburring of the molding resin, and surface finishing such as plating if the leadframe is not preliminarily surface-finished. Thereafter, the semiconductor device is cut off from the leadframe. For the case of surface mounting type, after the semiconductor device is cut off from the leadframe, it is subjected to a forming process according to a predetermined dimension of leads. More specifically, the outer leads horizontally projected out are bent downward, and then further bent in the horizontal direction, to thereby form a gull-wing geometry.
The outer leads are fixed to a substrate with the aid of solder fillets, when the semiconductor device is mounted on the substrate or the like. By the way, in some cases of such semiconductor devices, cut portions appeared in the process step of cutting off the semiconductor device from the leadframe may become the end portions of the leads without a further modification. These cases, however, raise difficulty in stably forming the solder fillets, due to influences of conditions of the cut surface of the end portions of the leads.
Japanese Laid Open Patent Publication No. 2005-209999 discloses a configuration of a semiconductor device having a molding resin for encapsulating a semiconductor chip, and a plurality of leads provided to the outer periphery of the molding resin, wherein the end portions of the leads are bent upward by the half die cutting process. It is reported that the solder fillets can be formed on the lower surfaces and the side surfaces including stepped portions of the leads, and can thereby improve adhesiveness of solder to the end portions of the leads.
Japanese Laid-Open Patent Publication No. H9-232499 discloses a configuration in which an inclined surface for reducing the thickness of the lead is formed in the mounting portion, to be placed on the pads, of the outer leads for external connection, formed by cutting with the aid of a dedicated die, and by bending according to a gull-wing form.
Japanese Laid-Open Patent Publication No. H8-172153 discloses a configuration of leads having notched portions formed in the lower surfaces thereof along a cutting line, and by cutting the outer leads along this line, so as to leave a plated film on the end surfaces of the leads with the aid of notched marks. It is reported that this structure makes it possible to leave a plated film on the end surfaces of the outer leads in a reliable manner.
Japanese Laid-Open Patent Publication No. H7-30042 discloses a leadframe configured as having grooves formed by machining from the top side, in the portions thereof which fall on the end portions of the leads after being processed into a lead form. It is reportedly made possible to form the solder fillets on the end surfaces of the leads in a reliable manner with this structure.
Japanese Laid-Open Patent Publication No. H7-211838 discloses a lead cutter for semiconductor device, composed of a die and a punch, configured as setting the blanking clearance between the punch and the die within the range from 14 to 21% of the total thickness of one of the leads and solder layers formed on the upper and the lower surfaces of the lead, disposing the punch as being facing the die, so as to freely movable in the vertical direction. It is reportedly made possible to incur plastic deformation to the solder layer on the upper surface of the leads, so as to form plating sag of the solder layer extending from the upper rim to the lower rim of the cut surfaces with this structure.
However, techniques disclosed in all of Japanese Laid-Open Patent Publication Nos. 2005-209999, H9-232499, H8-172153 and H7-30042 were in need of additional processes for altering geometry of the end portions of the leads. Examples of the necessary processes include etching and coining during manufacturing the leadframe, and preliminary processing in lead cutting. As a consequence, a problem arises in that the cost expands due to increased number of process steps.
In addition, the present inventors found out that it is important to increase the ratio of formation of sheared surface in the cut surface, for the purpose of raising the ratio of formation of plated film on the cut surface of the leads.